The present invention is directed to a skipped-stitch mechanism on a sewing machine having a needle bar oscillating in a longitudinal direction, a control device for producing lateral swing-out motions of the needle bar in order to make different zigzag stitches, and a coupling device coacting with the needle bar and operated by a second control device so as to intermittently separate the needle bar from its driving member under the control of a program device in order to skip the stitching.
Skip-stitch mechanisms are well known in the art. One embodiment is exemplified by West German Pat. No. 1,683,029. The coupling member is a horizontally-disposed swiveling lever which, in order to couple the needle bar with the driver, engages in a slot in the needle bar when the latter is in a given lateral swing position (zigzag stitch). The appropriate locking of the needle bar is effected through friction. Aside from the fact that the coupling slot weakens the needle bar, this mechanism has the considerable drawback that during the lifter motion of the needle bar the disengaged coupling lever wipes over the control arm and the friction pad provided for the locking of the bar exerts a continuous braking action. Another drawback is the release of the coupling on only one side of the swinging motion of the needle.
Therefore, an object of the present invention is to provide a skipped-stitch mechanism of the type referred to above which, independently of the swing-out position of the needle bar, enables the release of the positive coupling of the needle bar with the driver and simultaneously produces a positive locking of the disengaged needle bar in its upper final position. To this end, the skipped-stitch mechanism according to the present invention is characterized in that the coupling device is provided with a spring-loaded bolt positioned on the needle bar drive and engaged in a hole in the needle bar. The bolt is in operable engagement with a disengaging lever which, independently of the lateral position of the needle bar in the upper section of its path of motion, is operated by a program-controlled control lever in the direction of disengagement of the needle bar. The control lever acts simultaneously in its position of disengagement on a pawl provided for the disengaged needle bar and placed on the housing of the sewing machine in order to hold the needle bar in its upper final position.
It is essential that the disengagement occur immediately independently of the lateral position of the needle bar, which changes during the zigzag stitching. The spring-loaded bolt on the needle bar driver with a disengaging lever constitutes only a slight mass which is to be moved along with the needle bar, and a special advantage resides in the fact that the disengaged needle bar is constrained, that is to say, is positively held in its upper final position by a pawl and not, for example, through friction. It should also be recognized that a radial bore in the needle bar, which enables the pin to be engaged, does not weaken the needle bar nearly as much as a radial slot as utilized in the prior art.